1. Field of the Invention
The present invention relates generally to implantable medical devices, and more particularly, relates to implantable medical devices for the treatment of apnea.
2. Description of the Prior Art
The medical characteristics of sleep apnea have been known for some time. There are two generally recognized forms of the disease. The first is central sleep apnea, which is associated with the failure of the body to automatically generate the neuro-muscular stimulation necessary to initiate and control a respiratory cycle at the proper time. Work associated with employing electrical stimulation to treat this condition is discussed in "Diaphragm Pacing: Present Status", by William W. L. Glenn, in Pace, Volume I, at pages 357-370 (July-September 1978).
The second condition is known as obstructive sleep apnea. It is discussed at some length in "Obstructive Sleep Apnea: Diagnosis and Treatment", by Drs. Cook and Osguthorpe in Journal of South Carolina Medical Association, 81 (12): 647-651 (December 1985).
At present, a tracheostomy may be the treatment of choice for a number of patients when obstructive sleep apnea is severe. A less traumatic recent approach is continuous positive airway pressure (CPAP). This technique seeks to maintain upper airway patency with compressed air. More recently, some interest has been displayed in electrical stimulation of the muscle tissue along the upper airway during respiration. U.S. Pat. No. 4,830,008 issued to Meer discusses a technique for electrical stimulation of the muscles of the upper airway in synchrony with the respiratory cycle. U.S. Pat. No. 4,506,666 issued to Durkan discusses such stimulation in conjunction with pressurized airflow supplied by a respirator.
The electrical stimulation of the prior art techniques, however, are primarily concerned with causing contractile motion of the stimulated muscle. This means that the stimulation energy must necessarily be relatively large, and the effects of the stimulation are directly cognizable by the patient.
More significant is that prior art systems tend to be directed toward treatment of either central or obstructive sleep apnea. There exists no effective means for treating both conditions which are found together in a sizable number of patients.